Abstract:
Kazhdan's property (T) for groups is equivalent to the alternative that a representation of such a group either has an invariant vector or does not have even almost invariant vectors. It is shown that, under a somewhat stronger condition due to Żuk, a similar alternative holds for almost representations.
Keywords:group representation, almost representation, Żuk's condition, Kazhdan's property (T) for groups, Kazhdan constant, group $C^*$-algebra, Hilbert space, linear operator.